I can't remember which AS (Sheriam?), but one of them clearly said they allow no one who don't meet the strength standard to risk passing their test. They have a benchmark strength, and Daigian meets it, barely. The fact they have this standard and don't alter it is partly responsible for their dwindling numbers: they reject more and more candidates. Daigian is probably exceptional for the fact it's rare for women with barely meeting the standard to persevere, not get demolished by the prejudices against her strength and eventually pass the test. Nowhere it's suggested she's exceptional for having been allowed to pass the test despite not meeting the strength benchmark.

RJ was giving a reference to an inquiring reader. It would be totally worthless on its own if it excluded anyone with the shawl. It would be debatable if an Aes Sedai mentionned it in the series where it could be subject to contextual distortion or prejudices and all, but in a Q&A from RJ there's no doubt this includes all Aes Sedai.

The purpose of Daigian was manifold: serving as reference to give us a sense of how many women the WT rejects; implying that the testing puts too much weight on the ability to channel under stress (it's a good test to determine if a woman should be let to join a battlefield, it's a terrible test to judge if a woman should get the AS status) and blocks women who would have been fully trained as AS in the AOL - not to mention the dice are loaded because low standing women like Daigian need many times the intelligence, strength of character and sheer will of any high potential women to withstand a system which will seek to demolish their self-confidence and self-esteem. Her last purpose was to show how badly the Tower taught Nynaeve. Another purpose of Daigian, her first one in the series, was to show that Cadsuane had very different criteria than the WT's to judge the worth of sisters that she'd value a lot someone like Daigian over fairly strong (in OP) AS she judges weak in personality and absolutely unfit for the shawl. It's not that she believes the OP standards are wrong, it's that she believes the Tower no longer does its job at forming the stronger candidates. She considers the women strong in the power generally weak and flawed in character because their teachers made way too much of their OP potential and didn't care enough to hone the rest. It's why she's so judgmental with Nynaeve - the way she was (not) trained and educated properly by the sisters because she outclassed everyone alive in OP potential is to her symptomatic in an extreme way of what's wrong with the way today's AS are trained: you have to be weak to deserve the full exacting training/teaching everyone has a right to get, if you're too strong they'll turn corners, with Nynaeve to the point of sheer absurdity (AS barely bothered to train or teach her at all!). Nynaeve had a high potential even by AOL standards, and her likes had not been seen in over a 1000 years, and yet she's the woman the WT invested the least efforts in training properly (and not much better for Elayne and Egwene, also let too soon off the leash)... It's not only they put too much value on raw potential, it's also that you get the sense for many strong-ish sisters training Nynaeve properly would mean giving extra advantages to a woman who will soon stand above you. It also happened with women like Siuan and Moiraine, in a less extreme way. Moiraine had it right in NS though she didn't fully grasp the implications: your training really starts only once you've gained the shawl, and by then it's self-teaching. It's as if despite claiming the opposite the AS unconscious wish the stronger women to gain the shawl with the least additional advantages beside what they can't change - your raw potential - because the way the system works, you'll enter the hierarchy standing at an high rank right away, and they fear you, fear what will happen if they give you a full training that will make you formidable fairly young. The more devious and ambitious like Elaida even seek to bully recruits with more potential and put them in her debt, knowing it might come handy one day to balance the advantages you'll have over her. No wonder the more experienced sisters resent you rather then see in you someone to train the best they can. With Nynaeve that absurdity went overboard. The Yellows were wholly uninterested in her, knowing all too well she'd come to their Ajah and would get the shawl soon enough, and when she did she'd stand ridiculously higher than any but the Ajah leaders, and this is bad enough already, they have no interest to see you also enter their Ajah with a proper education and a potential honed as perfectly as the Tower can manage (the sort they gave to Daigian...), because then you'd be way too formidable to oppose. It's a vicious circle: the more it goes on, the less well-trained women are each generation (and not only in the OP - the weaves they all learn). Now it's up to a woman with mere months of OP training to make calls on how AS should be trained (and she's about to make a very bad call with her plan to raise as many new sisters as she can... she'll end up with a whole crop of even more badly trained/educated sisters after TG... as happened after the Trolloc Wars, leading to a sharp decline phase in the Tower. Except of course the whole idea is to justify some radical changes by the end of the series, so Egwene's bad calls are necessary plot devices).

Even in Cadsuane's days it was like this, though the vicious circle logic helping, it's probably worse now. Her real training, the one the envious sisters she had for teachers denied her, she got from the toothless wilder.

The whole absurdity of Nynaeve's situation is clearest when you consider she could have chosen any Ajah. She could have become the highest standing Green, able to pull rank in all sort of situations, with barely scraps of understanding of warfare. Do you see Nynaeve as a potential AS leader discussing military plans with the likes of Bryne or Bashere? She could have become the highest standing White sisters, an Ajah that fancies itself the group of finest logicians and philosophers, fountains of wisdom, yet Nynaeve would have had barely scraps of knowledge of logic and philosophy. She'd have been the highest ranking white... and the one the Ajah shivered every time she opened her mouth in public... She could have been the highest Gray... the one who would have run for cover if nobles asked her to judge their case involving intricates laws she'd never even heard of, or the highest Brown whose barely read any book and has no idea what being a scholar demands....

It's in sharp contrast with the systems of the WO who give their best to any apprentice. The SF have somewhat the opposite flaw to the WT's system: they give all they have to their very strong but see the weakest ones as not worth such efforts.